Please help. I have searched and searched online, have seen a variety of answers-some didnt even make sense.
The problem: The engine has a running rich smell at idle. So much so it stings my eyes at times, and have seen other peoples reactions to it as well! It has black powdery carbon on the plugs.
It isnt: the oxygen sensor-thats brand new almost. The truck has all new sensors, even a new computer, new plugs, wires cap and rotor. The computer once threw the code that the air/fuel mix is too rich. After reading this forum, I figured it was the Plenum gasket. I fixed that, the gasket was blown and I get much better acceleration now.
Here is whats odd. Before I fixed the Plenum, it ran rich at Idle still, but sometimes ran so bad at idle I had to pump the gas to get the truck started! Other times it idled fine. After fixing the plenum, at first it would stall when I came to intersections. Now, every time I come to a stop the idle drops way down then comes back up. After it does this it runs rough, then the over rich smell. It does this on every stop now. On acceleration it has great power and runs great down the highway.
I have read it could be the Fuel vapor canister, which I do smell a gas odor around it (unless thats the fuel tank) and Im going to investigate that further. I also read it could be-restriction of the air cleaner (which looks fine) and clogged cat (but seems fine as well)/ Also to note-I have completely cleaned the throttle body as well.
Anyone else have this problem? I have read several posts on this that ended up going no where with no answer! Please help

 

I had problems similar to this and the guys here suggested the Engine Coolant Temp Sensor, amongst other things, the temp sensor is to the right and behind the thermostat when viewed from the front, it along with a few other things fixed mine right up. Sounds like the Cat is plugged to me but I am FAR from the final word as to these motors!

I was also made aware of the TPS and IAC could be bad as I had replaced the cam sensor, cat, 02 sensors, plugs, cap, rotor, cleaned the TB and a new air filter previously. The new IAC helped some but the Temp Sensor was the big culprit.

I'm sure the guys will be along shortly to help you out.

Larry

 

It sounds like an upwind o2 sensor.. what brand did you use to replace the bad one?

 

unplug your o2 sensor, see if it improves

 

I think the new one is a Bosch Oxy sensor. Ill try the disconnect as well

 

Bosch has a history of bad sensors right out of the box... NGK/NTK or densco for these trucks.

 

Bosch and these trucks do not mix, for anything, spark plugs, O2 sensors, etc. I wouldnt be surprised if thats your problem right there.

 

Thanks guys. I tried un-plugging the oxy sensor this afternoon. Made no difference, but did try to stall more. So it must have been working a little. would the EGR valve have something to do with the carbon fouling? I have a new one on there. Maybe blocking that off completely would stop carbon fouling-or is that not recommended?

 

I took this truck to a auto repair. Even though I had replaced all sensors, they claimed the engine coolant sensor was bad. I told him I replaced it recently, he said its wasnt the one on the engine (????). Ok He said thats why the rpms were unsteady while idling. He said the Oxygen sensor was fouled, so they replaced that. Then they cleaned the fuel system and injectors, and told me it still wasnt perfect, they thought it was the timing chain worn (maybe) hahahaha...uh no. I get the truck and it dies everytime I come to a stop now. Now, I get a code the map sensor is out, so they either put a bad one in, or they ruined it somehow because I never had a code for that before. Once the rpms are over 900 rpms, its smooth, but its now gulping gas away. I sent a complaint to the company so now they are supposed to check it out more. They better for 600 bucks!
If this dont workout, Im seriously thinking of trashing the computer, sensors, and EFI system and switch it to carburator!! I am so sick of this crap!

 

You have two coolant temp sensors, both are on the intake manifold. (one is just for the gauge in the dash) That's it.

Sounds like they didn't know what was wrong with it either, and simply shotgunned parts at it...... for the money you have into it, they should just fix it, and NOT charge you anything more.